The present invention relates to a water purifying method and an apparatus used therefor, and particularly to a water purifying method capable of increasing purifying efficiency and facilitating maintenance by use of an elongated, closed water channel.
A conventional basic system for purifying sewage or water in a fish tank or the like generally includes the following steps: physically removing a solid matter through a screen (filter); decomposing ammonia contained in the contaminated water into nitrous acid, and then converting a nitrate by oxidizing (or nitrifying) the ammonia using aerobic bacteria such as active sludge.
However, nitrification of ammonia only is insufficient for purifying water, because nitrate generated in water increases acidity of the water, and causes eutrophication. Accordingly, it has been attempted to remove (denitrify) the nitrate, more specifically, convert the nitrate into a nitrogen gas by action of anaerobic bacteria, thereby more completely to purify the water. Moreover, in the nitrification step using aerobic bacteria, a large amount of oxygen must be supplied to activate the aerobic bacteria. In some cases, this oxygen must be provided by using fluidizing or stirring means.
The denitrification step using anaerobic bacteria, however, should be carried out without oxygen, for example, by closing a denitrification tank or by temporarily stopping the water flow. It is very difficult to continuously establish these inconsistent conditions of nitrification and denitrification in the same equipment. This has limited practical use miniaturization of the conventional water purifying apparatus.
The present invention provides a method which comprises propagating, at the first stage of an elongated, closed water channel, aerobic bacteria for realizing nitrification, and then disposing, at a later stage (by which point oxygen is almost consumed by the aerobic bacteria), a second stage having anaerobic bacteria. By this method, the water flowing through the apparatus, will nitrify and then denitrify a specific amount of water successively flowing in the same water channel.
The use of the elongated, closed water channel makes it possible to prevent a so-called xe2x80x9cchannel phenomenonxe2x80x9d in which water flows only through a specific portion of a filter material, thereby help to use the entire filter medium. It also makes it possible to locate aerobic and anaerobic bacteria at different places in the same water channel, and thereby to obtain nearly perfectly purified water. The method permits miniaturization of the apparatus.